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1. Field of the Invention
The present invention relates to pyrometallurgical processing, including a process for producing aluminum metal and titanium tetrachloride from clays containing hydrous aluminum silicate and titanium. More particularly, the present invention relates to a process for improving yield in removing iron in the purification of aluminum chloride through the addition of iron particles or equivalent iron containing compounds. The reactive sublimation of impure aluminum chloride with a reducing agent of iron in finely divided form substantially purifies the impure aluminum chloride. The purified aluminum chloride can then be effectively smelted into aluminum by aluminum chloride smelting processes.
2. Description of Related Art
For over one hundred years, a customary method of producing aluminum commercially has been the well-known Hall-Heroult process in which alumina dissolved in a fluoride bath (principally cryolite) is reduced electrolytically. The Hall-Heroult process requires a feed of pure alumina, which is typically produced commercially by the Bayer process, which in turn requires a feedstock of high grade bauxite. Bauxite occurs in few areas of the world, and no commercial deposits exist in North America.
Production of aluminum by electrolysis of aluminum chloride dissolved in a molten electrolyte composed of one or more halides having higher electrodecomposition potential than aluminum chloride (e.g., alkali metal halide or alkali earth metal halide) has been described in the literature; for example, Z. fur Elektrochemie, Vol. 54, pp. 210-215, U.S. Pat. Nos. 1,296,575, 1,854,684, 2,919,234, 3,103,472, 3,725,222 and Canadian Patent No. 502,977. This aluminum chloride smelting was initially thought to promise higher energy efficiency than the Bayer-Hall-Heroult process, but the promise went unrealized commercially because of problems and costs related to impurities in the aluminum chloride.
Purity of aluminum chloride feedstock is deemed essential to successful commercial production of aluminum by electrolysis of the aluminum chloride in a molten electrolyte. U.S. Pat. No. 3,725,222, assigned to Alcoa, disclosed that it is highly important that the concentration of metal oxides in the bath, expressed as oxygen, be kept below 0.25 percent by weight, and preferably below 0.1 percent by weight, and more preferably, below 0.05 percent. Alcoa""s smelting process utilized Bayer alumina that was chlorinated by first spraying fuel oil onto hot alumina particles, which pyrolized the oil into reactive carbon deposited on the alumina particle surfaces, and then reacting the carbonized aluminum with chlorine. Alcoa did not use aluminum chloride from low grade clays.
Production of purified aluminum chloride from low grade aluminous materials, including kaolin clays, bauxites, aluminum phosphate, shale and other raw materials by a carbo-chlorination process, followed by oxidation of the purified aluminum chloride into high grade aluminum oxide is disclosed in U.S. Pat. Nos. 3,935,297, 3,937,786, 3,938,969, 3,950,485, 3,956,454, 4,035,169, 4,082,833, 4,083,923, 4,083,927, 4,203,962, 4,220,629, 4,514,373, 4,695,436, and 4,710,369. This process of carbo-chlorination was directed to replacing bauxite-based aluminum oxide with aluminum oxide produced by the oxidation of purified aluminum chloride. For example, U.S. Pat. Nos. 4,514,373 and 4,695,436 disclose a process for producing substantially pure aluminum chloride by subliming and desubliming solid crude metal chlorides, which have been combined with aluminum powder. The other metal chlorides are separated from the aluminum chloride. But this process is less cost effective because of the cost of aluminum powder. Also, any excess aluminum powder is not easily or cost effectively recoverable.
Accordingly, it is an object of the present invention to provide a more cost effective process for purifying aluminum chloride. It is further object of the invention to improve the production of purified aluminum chloride for use in the production of aluminum by electrolysis of aluminum chloride.
It is another object of the invention to provide a continuous process for producing aluminum from low grade aluminous materials.
It is yet another object of this invention to provide a process for obtaining titanium tetrachloride and silicon tetrachloride from low grade aluminous materials containing titania and silica.
These and other objects will be apparent from the description of the invention and the claims, taken in conjunction with the drawing, or by practice of the invention.
What is provided is a process in which aluminous ore, a carbon source, and other raw materials are used to make and purify aluminum chloride, titanium tetrachloride, and silicon tetrachloride. Ores usable in this invention are those containing aluminum oxides and silicates that may be carbo-chlorinated using the instant catalyst at a temperature range of approximately 500xc2x0 C. to approximately 1000xc2x0 C. Examples of such ores include kaolinitic, illitic, and other aluminum clays; bauxite clay and other bauxite ores; siliceous bauxites and sillimanites; kyanites; aluminus shale, slates and fuel ashes; nepheline syenties; and anorthosite. The carbon source which is used in the drying process may be a carbonaceous gas such as carbon monoxide or carbonyl chloride or phosgene, or it may be one of a number of coal cokes or chars, including cokes and chars from lignite, petroleum coke and peat. The process is generally comprised of the following steps:
Step 1xe2x80x94Drying
The aluminus ore is fed into a dryer where it is dried with off gases from a calciner at a temperature range between approximately 100xc2x0 C. and 200xc2x0 C. The dryer removes the free water from the aluminous ore. The carbon source is fed to a dryer where it is dried under controlled atmosphere, low in oxygen, between approximately 100xc2x0 C. and 150xc2x0 C.
Step 2xe2x80x94Calcination
The pyrometallurgical calcination step utilizes elevated temperatures to remove the chemically bound water from the aluminus ore at a temperature of between 600xc2x0 C. and 950xc2x0 C. The ore must be dried and removed of free water and chemically bound water to prevent objectionable hydrolysis of metal chlorides or the formation of corrosive hydrochloric acid.
Step 3xe2x80x94Chlorination
During the chlorination step, a chlorinating agent such as dry chlorine gas and/or a functionally equivalent chlorine compound is combined with the ore, catalyst, and reductant, at elevated temperature of 600xc2x0 C. to 1000xc2x0 C.
Step 4xe2x80x94Condensation
The solids condensation system receives the hot vapors from the chlorinator and recovers heat and condenses crude, impure aluminum chloride. A heat exchanger and aluminum chloride condenser are used to the solids condensation system.
Step 5xe2x80x94Liquids Condensation
The uncondensed vapors from the solids condensation unit flow into the liquids condensation system for condensation of approximately 98% of the silicon tetrachloride and 98% of the titanium tetrachloride.
Step 6xe2x80x94Silicon Tetrachloride and Titanium Tetrachloride Purification
The liquid mixture recovered in Step 5 is directed to conventional rectification and condensation equipment for separation of the silicon tetrachloride and titanium tetrachloride and further purification of silicon tetrachloride and titanium tetrachloride.
Step 7xe2x80x94Aluminum Chloride Purification (Blender)
During the blending operation, the crude solid aluminum chloride compound and powdered metal, preferably iron at the feed rate of 1-5 molar relative to the metal impurity level in the crude aluminum chloride, are fed into a blender.
Step 8xe2x80x94Multi-State Sublimation
A first sublimer commonly used in sublimation processes receives the mixture from the blender and, operating at a temperature of at least 180xc2x0 C. and a pressure of at least one atmosphere, the solid aluminum chloride sublimes to aluminum chloride vapor at these conditions. These steps of sublimation and desublimation are repeated until high purity aluminum chloride is achieved.
Step 9xe2x80x94Granulated Metal Reactor
The pure aluminum chloride from the sublimer may be directed through a granulated metal reactor where is comprised of solid granules or activated granular metal which removes the sulfur impurities and non-aluminum metal chloride traces.
Step 10xe2x80x94Aluminum Chloride Condenser
The purified aluminum chloride vapor/nitrogen mixture is then directed into the condenser where the aluminum chloride solidifies at a temperature between 40xc2x0 C. and 180xc2x0 C.
Step 11xe2x80x94Aluminum Chloride Smelting
The purified solid aluminum chloride is then directed to closed smelting cells where the aluminum chloride is dissolved in a molten electrolyte comprised of one or more halides having higher electrodecomposition potential than aluminium chloride and is converted by electrolysis into aluminum metal and chlorine.
Step 12xe2x80x94Chlorine Recovery
Chlorine from the electrolysis cells is cooled, compressed, liquefied and stored for recycle to the second fluidized bed reactor.
Step 13xe2x80x94Pollution Control
The pollution control system scrubs the waste gases from the system with an alkali solution before they are released to the atmosphere, where they then contain mostly carbon dioxide.